1. Field of The Invention
The present invention relates to TFI-OFDM transmission and reception systems and methods thereof for mitigating interference from adjacent piconets in multi-band orthogonal frequency division multiplexing for ultra wide band (UWB) transmissions.
2. Description of the Related Art
In a wireless communication environment utilizing a wide frequency band, such as the ultra wide band (UWB) 3.1˜10.6 GHz, the entire frequency band is divided into a single sub-band or a finite number of sub-bands. A continuous wave is not used in a time domain, of which signals exist in every time domain, but rather, a form of a wave packet is used, of which signals exist in a certain region of the time domain. In a single band system that uses a single frequency band, an impulse utilizing every frequency of the UWB is adopted for transmitting and receiving signals. However, the single band system tends to be vulnerable to interference from other systems. To address this shortcoming, a multi-band system utilizes a plurality of sub-bands as the need arises to effectively cope with the interference. However, when using a RF circuit consisting of a single oscillator, the performance of the multi-band system may be seriously degraded since the energy furnished from the multi-path fading channel reaches about 20% of the entire energy. To overcome this shortcoming, the Texas Instrument (TI) Co. suggested a time frequency interleaved-orthogonal frequency division multiplexing (TFI-OFDM) system for the transmission scheme.
FIGS. 1A and 1B illustrate data spectrums in the frequency domain which are transmitted according to the conventional TFI-OFDM transmission scheme.
FIG. 1A illustrates a 55 Mbps mode of the transmission scheme, in which only a half (½) of the positive frequency domain carries actual data, and the remaining half (½) of the positive domain carries a copy of the actual data. The negative frequency domain carries a complex conjugate of the data in the positive domain. FIG. 1B illustrates 110 Mbps and 200 Mbps modes, in which the positive frequency domain carries the actual data and the negative frequency domain carries the complex conjugate of the actual data.
FIG. 2 illustrates a transmission scheme extended in the frequency domain according to the conventional TFI-OFDM transmission system. Shortcomings of the conventional transmission system are described with reference to FIG. 2. Piconet A has a transmission channel {f1, f2, f3, f1, f2, f3, . . . } and piconet B has a transmission channel {f3, f2, f1, f3, f2, f1, . . . } by using three frequency bands f1, f2, f3. As shown in FIG. 2, piconets A and B collide with each other. For example, the OFDM symbol A2 of piconet A, which is transmitted in the frequency band f2, collides with the OFDM symbol B2 of piconet B. The collided OFDM symbols cannot be recovered at a receiving side.
Accordingly, there is a need to mitigate the effect of collisions resulting from adjacent simultaneously operating piconets (SOPs) in the convention TFI-OFDM system.